Transducer assembly, ultrasonic atomizer and fuel burner

Abstract

A transducer assembly includes a first half wavelength double-dummy section having a pair of quarter wavelength ultrasonic horns and a driving element sandwiched therebetween. A second half wavelength stepped amplifying section extends from one end of the first section and has a theoretical resonant frequency equal to the actual resonant frequency of the first section. When used as a liquid atomizer, the small diameter portion of the stepped amplifying section has a flanged tip to provide an atomizing surface of increased area. To maintain efficiency, the length of the small diameter portion of the second section with a flange should be less than its length without a flange. A decoupling sleeve within an axial liquid passageway eliminates premature atomization of the liquid before reaching the atomizing surface. In a fuel burner incorporating the atomizer, ignition electrode life is increased by locating the electrodes outside the normal flame envelope. During the ignition phase, drive power to the atomizer is increased to widen the spray envelope to the location of the electrodes. A variable orifice controls combustion air flow in accordance with fuel rate while maintaining constant lower speed. Either three-step or continuous fuel rate modulation saves fuel and reduces pollution.

What is claimed is: 
     
       1. A transducer assembly comprising: a first section in the form of a symmetrical double-dummy ultrasonic horn having a driving element sandwiched therein, said first section having an empirically measured characteristic resonant frequency and   a second section including an amplification step, wherein the theoretical resonant frequency of the second section matches the empirically measured frequency of the first section.   
     
     
       2. An ultrasonic transducer including a first driver section and a second half-wavelength output section having a large diameter segment of length A extending from the driver section, a small diameter segment of length B extending from said large diameter segment, and a displacement antinode at the free end of the small diameter section comprising a flanged tip of thickness C, the improvement wherein A/B+C>1. 
     
     
       3. An ultrasonic transducer according to claim 2 wherein said flanged tip comprises an atomizing surface, said flange being of sufficient thickness to move as a rigid plane during vibration of the transducer. 
     
     
       4. An ultrasonic transducer assembly including a front ultrasonic horn section, a rear ultrasonic horn section, a driving element having at least one piezoelectric disc sandwiched between the front and rear ultrasonic horn sections, means for clamping the front and rear ultrasonic horn sections against the driving element, and an output section extending from the front ultrasonic horn section and terminating in an atomizing surface, wherein the improvement comprises: annular sealing means of compressible elastomeric material surrounding the at least one piezoelectric disc between the front and rear ultrasonic horn sections, said sealing means having an inner periphery which, in the unstressed condition, conforms to the shape of but is slightly greater than the periphery of the piezoelectric disc, and the compression exerted by the clamping means being sufficient to provide good acoustic coupling between the driving element and the front and rear ultrasonic horn sections when the inner periphery of the sealing means lightly contacts the outer periphery of the piezoelectric disc.   
     
     
       5. A transducer assembly comprising: a first section including a rear ultrasonic horn having a flanged portion at one end thereof, a front ultrasonic horn having a flanged portion at one end thereof, a driving element comprising a pair of piezoelectric discs and an electrode positioned therebetween, said driving element being positioned between the flanged portions of said front and rear horns, and means for clamping the flanged portions of said front and rear horns in compression against said driving element, said first section having an empirically measured characteristic resonant frequency; and   a second section including a large diameter portion of length A integrally formed with the front horn of said first section, a small diameter portion of length B extending from said large diameter portion, the interface between said large diameter and small diameter portions constituting a step for amplifying vibratory motion at said atomizing surface, said second section having a theoretical resonant frequency matching the empirical resonant frequency of said first section.   
     
     
       6. An ultrasonic transducer according to claim 5 comprising a rigid flanged tip of thickness C on the forward end of said small diameter portion, said tip having an atomizing surface, wherein the second section is a half wavelength section and A>B+C. 
     
     
       7. An ultrasonic transducer according to claim 5 wherein the second section has a flanged tip comprising a vibrating surface capable of causing atomization in a liquid, and the transducer further comprises means for delivering liquid to said atomizing surface, said liquid delivery means including a passage extending through said second section to said atomizing surface and a decoupling sleeve mounted within said passage and extending to said atomizing surface for acoustically isolating the interior surface of said passage from liquid flowing therethrough. 
     
     
       8. A transducer assembly according to claim 5 wherein the means for clamping the flanged portions of said front and rear horns in compression against the driving element comprises a plurality of assembly bolts inserted in spaced relation through corresponding holes in the flanged portions of the front and rear horns. 
     
     
       9. A transducer assembly according to claim 8 further comprising: annular sealing means of compressible elastomeric material surrounding the piezoelectric discs between the flanges of the front and rear horns for preveinting liquid from contacting the piezoelectric discs, said sealing means having an inner diameter which, in the unstressed condition, is larger than the outer diameter of each piezoelectric disc, such that predetermined compression exerted by the assembly bolts sufficient to provide good acoustic coupling between the driving element and the front and rear horns causes the inner circumference of the sealing means to lightly contact the outer circumference of each piezoelectric disc.   
     
     
       10. A transducer assembly according to claim 8 further comprising a mounting ring having a plurality of threaded holes aligned with the assembly bolt holes in the flanged portions of the front and rear horns, the mounting ring being clamped to the front face of the flanged portion of the front horn by engagement of the assembly bolts in the respective threaded holes. 
     
     
       11. A transducer assembly according to claim 8 wherein the first and second sections are half wavelength sections. 
     
     
       12. A method of making a high efficiency piezoelectric ultrasonic transducer comprising the steps of constructing a first transducer assembly section in the form of a double-dummy ultrasonic horn comprising a driving element, two identical front and rear horn sections, and means for clamping the horn sections to the driving element;   empirically measuring the resonant frequency of said first assembly section; and   constructing a high efficiency ultrasonic transducer comprising a first section identical to the first transducer assembly section and a second section added to the front horn section of the first transducer assembly section, the second section including an amplification step and having a theoretical resonant frequency equal to the empirically measured frequency of the first transducer assembly section.   
     
     
       13. The method of claim 11 wherein the second section is constructed integrally with the front horn section.